It is frequently desired to expand a tube radially to form a leak-proof joint between the exterior of the tube and a surrounding member. Tube expansion is conventionally produced by either roller swaging or hydraulic swaging. Roller swaging employs a mechanical implement which is inserted in the tube and pressed against the tube surface, forcing the tube wall outwardly. The implement or roller is repeatedly passed over the interior tube surface until the desired expansion has been produced.
Hydraulic swaging, which is generally superior, particularly for high pressure applications in small diameter tubes, employs a mandrel which is inserted in the tube and employed to seal two ends of an elongated annular volume between the outside of the mandrel and the inside of the tube. Hydraulic fluid under pressure, which may be as high as 30,000 psi or more, is then introduced to the annular volume, forcing the tube to expand.
One environment in which the use of swaging to expand tubes radially plays a roll of great importance is in the construction of heat exchangers, particularly those heat exchangers intended for use in nuclear power plants. Hydraulic swaging, using pressures among the highest attainable, is found to be the most effective for this demanding application. A problem that arises, however, is that of anchoring the tube within the tube sheet in preparation for the high pressure swaging operation.
An objective of the present invention is to provide a new and improved method and apparatus for expanding a tube radially. A further objective is to provide such a method and apparatus that are particularly suitable for use in connection with the anchoring of tubes in a tube sheet in preparation for a subsequent swaging operation.